GGA-SCAN failure to describe multiple valance states of copper

The Strongly Constrained and appropriately normed meta-GGA (GGA-SCAN) is a parameter-free first principles density-functional celebrated for correctly describing spectral properties of strongly correlated systems. GGA-SCAN correctly predicts the gapping of e.g. Mott insulators and cuprite superconductors, where conventional GGA functionals fail. We test GGA-SCAN's predictive power for thermochemical formation enthalpies of cuprous oxide Cu₂O, cupric oxide CuO, and YBa₂Cu₃O_7-δ (YBCO), and find that SCAN fails to predict the relative stability of Cu^+I(d¹⁰) vs. Cu^+II(d⁹), excessively stabilizing Cu^+II(d⁹) such that Cu₂O is thermochemically unstable. Ensuingly, GGA-SCAN also predicts unphysical defect structures for YBCO at small δ. While conventional GGA functionals can be corrected for both spectral and thermochemical properties by Hubbard-U corrections, GGA-SCAN cannot.